When the Y/C separation is performed for a composite video signal, harmful influences such as dot crawls (which are also called “cross luminance interferences”) and cross color interferences occur. The Y/C separation is classified broadly in three types, and these three types of separation are referred to as one-dimensional Y/C separation, two-dimensional Y/C separation, and three-dimensional Y/C separation, respectively. Here, three-dimensional frequency characteristics of two-dimensional Y/C separation are shown in FIG. 17, as an example. FIG. 17 represents an NTSC signal in three-dimensional frequency space. In FIG. 17, a large rectangular parallelepiped 1001 in the center represents the band of the luminance signal, and hatched small rectangular parallelepipeds 1002 represent the bands of the color-difference signals. Further, rectangular parallelepipeds 1005 shown by dotted lines represent frequency bands extracted by a two-dimensional Y/C separation filter as the color-difference signal. It can be seen from FIG. 17 that when the color-difference signals have high frequency components in the vertical direction, higher frequency components of the color-difference signals that belong to the bands of the rectangular parallelepipeds 1002 and that lie off the rectangular parallelepipeds 1005 remain as luminance signal components. These frequency components of the color-difference signals that remain as the luminance signal at the Y/C separation cause dot crawls.
As a prior art video signal processing apparatus for reducing these harmful effects, a video signal processing apparatus that reduces the dot crawls is disclosed in Japanese Published Patent Application No. Hei.4-17485 (hereinafter, referred to as Reference No.1). In this video signal processing apparatus, saturation levels of color-difference signals are detected, and notch filtering is performed for a luminance signal according to the detected saturation levels, thereby reducing the dot crawls.
Further, as an apparatus for reducing cross color interferences, there is an apparatus that reduces cross color interferences of a carrier color signal, disclosed in Japanese Published Patent Application No. Hei.6-105322 (hereinafter, referred to as Reference No.2). This cross color reduction apparatus detects whether a carrier color signal of the present field and a carrier color signal of the immediately preceding field are not in inverted phases, and attenuates the present carrier color signal according to the detection result, thereby reducing the cross color interferences.
Further, as noises of the video signal, in addition to dot crawls and cross color interferences, there are time axis noises which are minute-level noises occurring at random in the temporal direction. As a prior art method for eliminating these time axis noises, there is, for example, a method described in “Multi-dimensional TV signal processing of TV pictures” (by Takahiko Fukinuki, published by Nikkan Kogyo Shimbun Ltd., pp.190–191).
The apparatus disclosed in Reference No.1 detects dot crawls using the saturation levels of color-difference signals. However, the dot crawls result, in cases where original color-difference signals have higher frequency components in the horizontal or vertical direction, from the higher frequency components of the color-difference signals remaining in the luminance signal after the two-dimensional or three-dimensional Y/C separation. Thus, dot crawls do not always occur in areas where the saturation levels of the color-difference signals are high. Therefore, in some cases, the apparatus that is disclosed in Reference No.1 cannot reduce dot crawls.
The apparatus disclosed in Reference No.2 compares the phases of a carrier color signal of the present field and a carrier color signal of the immediately preceding field, thereby detecting cross color interferences. However, for component video signals having demodulated color-difference signals, the method by which the phases of the carrier color signal of the present field and the carrier color signal of the immediately preceding field are compared with each other to detect cross color interferences, cannot be used. Therefore, the apparatus that is disclosed in Reference No.2 cannot reduce cross color interferences in component video signals after Y/C separation.